exact image of my back splash. Oil marks are expanding on the Non Flashy tiles.

You can try a poultice. However.......even when it has been well sealed, and I ASSUME your stone mosaic was sealed.....it will stain from oil or butter splashes.

After a while you tend not to notice the spots, but if concerned.......tape up foil near the cooker and cover the near splash when you saute or fry.

"In order to remove oil stains from tiles, first cover the tiles with
any kind of absorbent powder, like cornstarch or whiting. Wait for at
least half an hour and then brush away the powder. Spread the area with
more powder, and this time, leave it for twenty-four hours. The next
day, use a stiff brush to scrub your tiles with hot water and detergent.
Finish the process by rinsing your tiles and wiping them dry.

In the case of more stubborn grease stains, scrub the stains with a
mixture of poultice powder and acetone or amyl acetate (easily available
in any medicine shop) and then rinse it off." ( try cornstarch and cheap nail polish remover )

or

http://miraclesealants.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=66&Itemid=228

https://miraclesealants.com/index.php?option=com_content&view=article&id=21&Itemid=147

Remove the tiles behind the cooking zone and install a stainless sheet. They were not a suitable choice for a backslash in a kitchen that will actually get used.

oil the whole thing? actually, I think that would probably start to damage the tile, possibly even start to loosen it from the backing. sympathy that contractor and tile sales folk who should know better didn't mention that matte tires would be absorbent or didn't seal them. good luck.

Niranjan, I wish I had some insight but I’m actually faced with the same dilemma, with the exact same time. :-/ I was curious if you’ve found anything that works. I hope so - this tile is amazing (we always get compliments on it - I’m sure you do as well!). If you have found something that does work, would you care to share some advice? :) Thank you!